As the bandwidth of wireless systems expands, the ability to transmit digital video over wireless links has become easier and more cost effective. However, the data capacity of such wireless systems may vary over time depending on the surrounding conditions. This creates a significant challenge for developing a low-cost design that provides sufficient quality of service for consumer video applications.
Typical video compression techniques require buffering of multiple frames of data for the compression and decompression steps. Unfortunately, this buffering requires significant memory, which can add considerable cost to the system.
Furthermore, video compression techniques themselves tend to be variable rate, as the entropy of the source data tends to change on a line-by-line or frame-by-frame basis. This variable entropy also necessitates a dynamic adaptation algorithm.
Current video transmission systems use standard compression techniques such as MPEG2 (Motion Pictures Expert Group) and JPEG2000 (Joint Photographic Experts Group). MPEG2 uses compression techniques that take advantage of similarity between pixels as well as similarities between multiple frames of data. Because of this approach, any change in the compression algorithm would need to be made after several frames have been transmitted. This delay requires significant amounts of data to be buffered in the transmission system.
JPEG2000 uses compression techniques that are executed over an entire frame of data. This too requires at one complete frame of data to be transmitted before changing the compression algorithm.
Existing compression systems also use a fixed quantization and compression mechanism to enable either a constant bit rate data stream or a “variable” bit rate data stream. The definition of “variable” in this case is dictated by the algorithm, and there is no feedback mechanism from the channel to change the bit rate based upon channel conditions.
To enable low cost wireless transport of digital video, it would be desirable to have a method to dynamically adapt the data rate required for the video while buffering a small percentage of a single frame of video. This dynamic adjustment of the data rate should take place without any interruption of service to the viewer.